SoftDevice temperature acquisition

[SebastienTE]

Hello,

We're using a nRF52840 with a SoftDevice S140 enabled.

I would like to know if SoftDevice perfoms a temperature calibration and if HFCLK is set ot HFXO when calling sd_temp_get(). The documentation mentions that HFCLK is set for BLE radio operations but there is no detail for die temperature.

Is the HFCLK is resquested and then released by SoftDevice during a temperature acquisition? As in documentation it is only mentioned about TEMP Temperature sensor : "To achieve the measurement accuracy stated in the electrical specification, the crystal oscillator must be selected as the HFCLK source, see CLOCK — Clock control on page 85 for more information."

Is the temperature value is calibrated and so th ouput vlaue given by SoftDevice is linear ? The documentation provides only registers for linear compensation with a piecewise linear function, but there is no recommendation how to use it .i.e these values are take into account by SoftDevice or this is a matter for the application to get the characterisation of the tempreature curve from registers and apply correction with application of coefficients.

Thanks,

Sebastien

[Einar Thorsrud]

Hi,

The SoftDevice will not start the HFXO automatically when you call sd_temp_get(), so it is your responsibility to do that.

Regarding calibration, if using the LFRC the SoftDevice will take temperature into account to decite if it needs to calibrate the LFRC or not (see relevant configurations for that here). That is the only thing the SoftDevice use temperature for.

The temperature sensor on the nRF devices is primerily indended for use as in the case above, and therefor is not calibrated across temperature ranges. It is fairly good to detect changes in temperature, but not so much for measuring absolute temperatures. (See TEMP electrical specifications for details).

[SebastienTE]

Hello Einar, thanks a lot for your answer.

And about registers related to TEMP (piecewise linear function), what we have to do with these registers?

[Einar Thorsrud]

These registers are not documented publicly other than that they exist. They are not intended to be manipulated though, and should hold data from FICR. This is handled during startup (see erratum 66 and code writing to NRF_TEMP in system_nrf52.c).

[SebastienTE]

Hi Einar,

Thank you very much for your answer.

Sebastien